A transparent conductive film including a transparent electrode on a transparent film substrate is used in various fields such as solar cells, light-emitting elements, display devices, and touch panels. As transparent electrode materials, those containing indium oxide as a main component, such as indium-tin composite oxide (ITO) and indium-zinc composite oxide (IZO) are widely used because they have high transparency, low resistivity, and high reliability. However, with respect to the conductive oxide containing indium oxide as a main component such as ITO, an essential raw material thereof, i.e., indium, is an expensive rare metal, and there is concern about resource exhaustion. A conductive oxide has higher resistivity than metallic materials, and therefore has a problem that the transmission speed of a current between electrodes is low, so that the response speed becomes low as the device area is increased.
In view of the problems related to conductive metal oxides as described above, attempts have been made in recent years to use a patterned thin wire metallic material as a transparent electrode. For example, Patent Document 1 discloses a transparent conductive film including patterned thin metal wire composed of a silver halide photographic sensitive material, a silver nanowire, or the like, on a transparent base. However, silver is an expensive material, and is easily visible even when formed into a thin wire because it has a high metallic reflectance. Accordingly, it has been necessary to develop a transparent electrode including a thin metal wire made of copper as a material which has a lower metallic reflection and is less expensive and more versatile as compared to silver, and is also excellent in conductivity.
In the field of flexible printed wiring boards, a method has been put into practical use in which a copper wiring is formed on a polyimide film substrate by a photolithography method (e.g., Patent Document 2). Since a polyimide has a large dielectric loss tangent, and a large transmission loss in a high frequency region, an attempt has been made to form a copper wiring on a transparent plastic film substrate such as liquid crystal polymer or a thermoplastic cycloolefin (e.g., Patent Document 3).